1. Field of the Invention
The invention relates to a deflection circuit for generating a deflection current through a deflection coil to deflect an electron beam in a cathode ray tube, the deflection current having a scan period and a flyback period, the deflection circuit comprising: a series resistor arranged in series with the deflection coil to generate a feedback voltage related to the deflection current, a damping impedance arranged in parallel with the deflection coil, a drive circuit having an input terminal coupled to the series resistor to receive the feedback voltage, the drive circuit further being coupled to a conversion resistor to receive an input waveform, and having an output coupled to the series arrangement of the deflection coil and the series resistor, the drive circuit generating the deflection current in response to a difference between the input waveform and the feedback voltage, and current generating means for generating a correction current within the flyback period.
The invention also relates to a picture display apparatus comprising such a deflection circuit, and to an integrated circuit for use in such a deflection circuit.
2. Description of the Related Art
The Philips Semiconductors Application Note AN95029 "TDA 8350 and TDA 8351 deflection output circuits Application information" discloses an integrated power circuit for use in a raster scan circuit. The integrated power circuit has a first and a second output amplifier which are arranged in a bridge configuration to generate a deflection current through a raster scan deflection coil. The deflection current generates a magnetic field for deflecting electron beams in a cathode ray tube in the vertical direction. A measurement resistor is arranged in series with the deflection coil. Across this measurement resistor, a voltage is generated which is related to the deflection current through the deflection coil. The voltage across the measurement resistor is sensed with a first voltage-to-current converter which has a first and a second current output. To provide a feedback, the first current output is connected to an input of the first output amplifier, and the second current output is connected to an input of the second output amplifier. The integrated power circuit further comprises a second voltage-to-current converter which has two inputs for receiving an input waveform occurring across an input resistor. The second voltage-to-current converter has a first and a second current output. The first current output is connected to the input of the first output amplifier, and the second current output is connected to the input of the second output amplifier. The first and the second voltage-to-current converters are identical. The current outputs of the first and the second voltage-to-current converters, which are interconnected, supply output currents which have opposite polarities. In this way, the output voltages of the output amplifiers will be controlled such that the voltages across the measurement resistor and the input resistor are substantially equal.
A damping resistor is arranged in parallel with the deflection coil for smoothening switching points of the currents and voltages which occur in the raster scan circuit, as well to prevent ringing. However, this damping resistor deteriorates the flyback performance of the deflection circuit. Depending on the application, compressed lines, bright lines or flyback lines become visible.